The Mendelian Laws - This series introduces into classical genetics and is intended for use in all types of schools, especially high schools. The rich material allows the teacher to select according to the special situation. - Johann Gregor Mendel - Similarity of father and son - Identical (uniovular) twins - Intermediary inheritance in Mirabilis jalapa (Marvel of Peru) - Backcross in Mirabilis jalapa - Intermediary inheritance in chicken - Dominant inheritance of colour in pea flowers - Dominant inheritance of colour in pea seeds - Yields of Mendelians monohybrid crosses of peas - Dominant inheritance in stinging nettles - Dominant inheritance in corn (Zea mays) - Dominant inheritance in the snail Cepaea hortensis - Dominant inheritance in guinea pigs - Backcross of F1 in dominant inheritance - Backcross of F2 in dominant inheritance - Yields of pea crosses performed by various scientists - Dihybrid cross of peas - Distribution of characters in dihybrid cross of peas - Punnett square for dihybrid cross of peas - Backcross of dihybrid peas - Dihybrid inheritance in the snail Cepaea hortensis - Dihybrid inheritance in guinea pigs - Dihybrid inheritance in snapdragons - Punnett square for dihybrid cross - Distribution of characters in trihybrid crosses - Ratio of numbers in polyhybrid crosses - Distributing of parental genetic makeup to children - Genetic makeup common to a family - Additive factors - Supplementary factors in Lathyrus odoratus (Spanish vetch) - Polygeny in mammalian fur colour - Lethal factor in canary (Serinus canaria) - Lethal factor in yellow mice.

Variability Part I: The Modifications - Modificability is the changeability of the appearance or the ability of the whole genetic makeup (of the idiotype) to be expressed in the phenotype under the various developmental conditions, as well as internal and external influences. This is limited by the range of variation which itself is determined genetically. Modifications are changes of the phenotype which do not influence the idiotype. - Development of dandelion (Taraxacum officinale) in mountains and lowlands (experiments of Bonnier) - Different shape of plantain (Plantago) growing on track across the field and on forest margin - Different shape of pine growing singly and within the forest - Modifications of leaves on one branch - Modifications of leaves of a ginkgo tree - Gentiana plants from various sea levels - Stimulating and inhibiting effects on plants - Table of binomials and Pascal’s triangle - Binomial distribution or normal curve of variation for (a+b)4 and (a+b)10 - Variation curve for number of tail fin rays and lateral scales in two species of fish - Variation curve of the size in the identical progeny of a single Paramaecium - Unsuccessful selection in culturing Paramaecia - Fingerprints of identical twins - Starvation and mast form in sheep of the same age - Length of tadpole intestine depending on type of food - Growth speed of plaice depending on population density - Queen and worker bee, nutritional modifications - Changing modifications: biastrepsic and normal Dipsacus plants - Spring and summer form in the butterfly Araschnia levana - Cooling the pupa effects the colour of butterfly wings - Change of temperature modifies colour and size of an ichneumon wasp - Temperature and light modify the colour of petunia flowers - Temperature modification in Russian rabbit - Forms transitional between submersed and floating leaves - Leaves of young and old English ivy - Sex change depending on body length of a marine annelid - Phenotypic sex determination in the worm Bonellia - Transplantation of frog tissue to salamander tadpole - Mossy rose gall - Pine galls produced by aphids.

Variability Part II: The Mutations - Sudden changes in animals and plants which later proved to be hereditary are called mutations. They are either spontaneous or caused by mutagens, e.g. radiation, chemical substances, or change of temperature. Mutations are highly important for the further development of life, for breeding animals and culturing plants. The possibility of curing defective genes or purposefully changing intact or defective genes means total genetic manipulation of humans and organisms. This opens a both promising and shocking, but also utopian perspective. - Normal celandine (Chelidonium majus) and its laciniate mutant - Leaves of various plants and their laciniate mutant - Wild-type sheep and short-legged ancon mutant - Goldfish and its mutant - Wild-type carp and its mutants - Shape and skeleton of a normal and a brachydactylous human hand - Wild-type moth (Biston betularia) and its carbonaria mutant. Protective colour - Industry melanism of Biston betularia in Great Britain - Tailless mutant of domestic cat - Beetle with duplicated legs - Biastrepsis in Dipsacus and fasciation in Japanese spindle tree - Normal corn plants and gravitation-blind mutants - Normal snapdragon (Antirrhinum majus) and its cupuliformic mutant - Factor mutation of snapdragon. Shape and colour of flowers. Multiple alleles - Progressive reduction of wings in the fruit fly Drosophila. Multiple alleles - Fur colour of guinea-pig (black, brown, white). Multiple alleles - Diagram showing various types of gene mutations - Chromosome mutation in a female fruit fly Drosophila. Normal and mutated set of chromosomes - Relation between mutated chromosomes and eye size of fruit flies - Types of chromosome mutations - Inversion of chromosome segment in Drosophila. Inversion loop during chromosome pairing - Chromosome mutations in two varieties of peas. Karyograms and chromosome pairing during meiosis - Chromosome sets of epidermal cells and pigment pattern of the heads of haploid, diploid, and triploid salamander larvae - Haploid, diploid, triploid, and tetraploid plants of Solanum (nightshade) - Genome mutations in Drosophila - Leaf shape of stock (Matthiola) due to various surplus chromosomes - Normal shoot growing from the variegated leaf of Sansevieria nobilis. Proof of development of a chimera and of somatic mutation - Mutagenic effect of nitrous acid on DNA. Change of nucleic acid bases - Selection of deficiency mutants in bacteria - Metabolic block and accumulation of products. Tracing of metabolic chains.